Highly formable and intercrystalline corrosion-resistant AIMg strip

ABSTRACT

The invention relates to a cold-rolled aluminium alloy strip made of an AlMg aluminium alloy as well as a method for producing the same. Furthermore, corresponding components made from said aluminium alloy strips are also proposed. The problem for the invention of providing a single-layer aluminium alloy strip that is sufficiently resistant to intercrystalline corrosion and is nevertheless very formable so that even large-area deep-drawn parts, e.g. interior parts of motor vehicle doors, can be made with sufficient strength, is solved by an aluminium alloy strip made of an AlMg aluminium alloy as described herein.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a continuation of PCT/EP2013/067487, filedAug. 22, 2013, which claims priority to European Application No. 12 181356.2, filed Aug. 22, 2012, and PCT/EP2013/064736, filed Jul. 11, 2013,the entire teachings and disclosures of which are incorporated herein byreference thereto.

FIELD OF THE INVENTION

The invention relates to a cold-rolled aluminium alloy strip composed ofan AlMg aluminium alloy and a method for the production thereof.Furthermore, corresponding components produced from the aluminium alloystrips will be proposed.

BACKGROUND OF THE INVENTION

Aluminium-magnesium-(AlMg-)-alloys of the AA 5xxx type are used in theform of sheets or plates or strips for the construction of welded orjoined structures in ship, automotive and aircraft construction. Theyare characterised by high strength which increases as the magnesiumcontent rises. AlMg-alloys of the AA 5xxx type with Mg contents of morethan 3%, in particular more than 4%, have an increasing tendency towardsintercrystalline corrosion, when exposed to high temperatures. Attemperatures of 70-200° C., β-AlsMg₃ phases precipitate along the grainboundaries, which are referred to as β-particles and in the presence ofa corrosive medium can be selectively dissolved. The result of this isthat the AA 5182-type aluminium alloy (Al 4.5% Mg 0.4% Mn) having verygood strength properties and very good formability in particular cannotbe used in heat-stressed areas, where the presence of a corrosive mediumsuch as water in the form of moisture must be contended with. Thisconcerns in particular the components of a motor vehicle which normallyundergo cathode dip painting (CDP) and are then dried in a stovingprocess, as already due to this stoving process, normal aluminium alloystrips can become susceptible to intercrystalline corrosion.Furthermore, for use in the automotive sector, forming during themanufacture of a component and subsequent operational stressing of thecomponent must be taken into consideration.

The susceptibility to intercrystalline corrosion is normally checked ina standard test (NAMLT test) according to ASTM G67, during which thespecimens are exposed to nitric acid and the mass loss due to theintercrystalline corrosion is measured. According to ASTM G67, the massloss of materials which are not resistant to intercrystalline corrosion,is more than 15 mg/cm².

Sheet metal for the automotive industry, e.g. for internal door parts,must have very good formability. Here, the requirements are essentiallydetermined by the stiffness of the component concerned, with thestrength of the material playing only a subordinate role. The componentsoften undergo multi-stage forming processes, such as for example doorswith integrated window frame areas.

So, apart from the corrosion properties, the formability of the AlMgaluminium alloy also has a major influence on the usage possibilitiesfor this material. For example, the materials known so far have meantthat it is not possible for the side walls of a motor vehicle to bedeep-drawn from a single sheet, making not only reconstruction of theside wall but also additional process steps for providing the side wallof a motor vehicle necessary.

The forming behaviour can, for example, be measured in a stretch drawingtrial by an Erichsen cupping test (DIN EN ISO 20482), in which a testpiece is pushed against the sheet, resulting in cold forming. During thecold forming, the force and the force displacement of the test piece aremeasured, until a load drop occurs, caused by the formation of a crack.The SZ32 stretch drawing measurements quoted in the application wereperformed with a punch head diameter of 32 mm and a die diameter of 35.4mm with the help of a Teflon deep-drawing film to reduce friction.Further measurements of the deep drawability were performed using theso-called plane-strain-cupping test using a Nakajima geometry accordingto DIN EN ISO 12004 with a punch diameter of 100 mm. For this, specimenswith a specific geometry underwent drawing tests until a crack appeared,with the depth until cracking being used as a measure of the formabilityof the material.

From JP 2011-052290 A, an aluminium alloy strip for can lids is known,which is preferably load-resistant despite its small thickness. Here,the strip has a recrystallized microstructure.

Further, from EP 2 302 087 A1, a chassis part is known made from analuminium composite material, which has aluminium alloy layers as outerlayers. Due to the alloying constituents, the Al composite material ischaracterized by excellent strength values with a high corrosionresistance at low weight.

Composite material solutions composed of AA5xxx aluminium alloys with ahigh Mg content and outer aluminium alloy layers to protect againstcorrosion, however, have the disadvantages that manufacture is complexand additionally at joining points where the aluminium compositematerial joins to other parts, for example at cutting edges, drill-holesand breakouts, there is furthermore an increased danger of corrosion.

SUMMARY OF THE INVENTION

The present invention is therefore concerned with single-layer aluminiummaterials. On this basis, the object of the invention is to provide asingle-layer aluminium alloy strip, having sufficient resistance tointercrystalline corrosion but nevertheless having good formability, sothat large-area, deep-drawn parts, such as interior parts of motorvehicles doors, with sufficient strength can be provided. Furthermore, amethod will be indicated with which single-layer aluminium alloy stripscan be produced. Finally, components produced from the aluminium alloystrips according to the invention will be indicated.

According to a first teaching of the present invention, the objectindicated is achieved by a cold-rolled aluminium alloy strip composed ofan AlMg aluminium alloy, wherein the aluminium alloy has the followingalloying elements:

-   -   Si≦0.2 wt. %.    -   Fe≦0.35 wt. %,    -   Cu≦0.15 wt. %,

0.2 wt. %≦Mn≦0.35 wt. %, 4.1 wt. %≦Mg≦4.5 wt. %,

-   -   Cr≦0.1 wt. %,    -   Zn≦0.25 wt. %,    -   Ti≦0.1 wt. %,        the remainder being Al and inevitable impurities, amounting to a        maximum of 0.05 wt. % individually and a maximum of 0.15 wt. %        in total, wherein the aluminium alloy strip has a recrystallized        microstructure, the average grain size of the structure ranges        from 15 μm to 30 μm, preferably from 15 μm to 25 μm and the        final soft annealing of the aluminium alloy strip is carried out        in a continuous furnace.

It has been found that within the specification of the AA5182-typealuminium alloy, there is a specific, narrow, alloying range whichoffers sufficient resistance to intercrystalline corrosion and at thesame time, by taking into account certain constraints, such as forexample the average grain size and the type of final soft annealing,results in an exceptional forming behaviour. In particular, thecombination of the average grain size with the claimed alloying elementsof the aluminium alloy of the aluminium alloy strip means that degreesof formability can be achieved allowing the production of large-areadesign, deep-drawn sheet aluminium products with sufficient strength. Inparticular it has been found that the use of a continuous furnace ratherthan the normal coil annealing performed in a chamber furnace provides afurther significant increase in formability.

According to a first configuration of the aluminium alloy strip, thealuminium alloy also has one or more of the following restrictions tothe contents of alloying elements:

0.03 wt. % Si≦0.10 wt. %,

-   -   Cu≦0.1% preferably 0.04%≦Cu≦0.08%,    -   Cr≦0.05 wt. %,    -   Zn≦0.05 wt. %,

0.01 wt. %≦Ti≦0.05 wt. %

Restricting the alloying content for copper to a maximum of 0.1 wt. %leads to an improvement in the corrosion resistance of the aluminiumalloy strip. A Cu content of 0.04 wt. % to 0.08 wt. % ensures that thecopper contributes to an increase in strength, but that nevertheless thecorrosion resistance is not reduced too sharply. Silicon, chromium, zincand titanium contents higher than the values indicated lead to aworsening of the formability of the aluminium alloy. The amount ofsilicon present in the alloy of 0.03 to 0.1 wt. %, in combination withthe iron and manganese components in the stated quantities, inparticular leads to relatively evenly distributed, compact particles ofthe quaternary α-Al(Fe,Mn)Si-phase, increasing the strength of thealuminium alloy, without negatively influencing other properties such asthe formability or corrosion behaviour.

Titanium is normally added during continuous casting of the aluminiumalloy as a grain refiner, for example in the form of titanium boridewire or rods. Therefore in a further embodiment the aluminium alloy hasa Ti content of at least 0.01 wt. %.

A further improvement in the corrosion behaviour and the formability ofthe aluminium alloy strip can be achieved by the aluminium alloy alsohaving one or more of the following restrictions to the contents ofalloying elements:

-   -   Cr≦0.02 wt. %,    -   Zn≦0.02 wt. %

It has been found that chromium in contents below the contaminationthreshold of 0.05 wt. % significantly influences the formability of thealuminium alloy strip and therefore should be contained in the smallestpossible proportions in the aluminium alloy of the aluminium alloy stripaccording to the invention. The zinc content is set at below thecontamination threshold of 0.05 wt. %, in order not to impair thegeneral corrosion behaviour of the aluminium alloy strip.

It has furthermore been found that iron within the values permittedaccording to the AA5182-type aluminium alloy in conjunction with siliconand manganese contents as described above has an effect on theformability. In combination with silicon and manganese, iron contributesto the thermal stability of the aluminium alloy strip, so thatpreferably the Fe-content of the aluminium alloy strip according to anext configuration is 0.1 wt. % to 0.25 wt. % or 0.10 wt. % to 0.20 wt.%.

The same also applies to the Mn content of a further configuration ofthe aluminium alloy strip, which should preferably be limited to 0.20wt. % to 0.30 wt. %, in order to achieve optimum formability of thealuminium alloy strip.

An especially good compromise between the provision of high strengthproperties, good corrosion resistance to intercrystalline corrosion andimproved forming properties can be achieved according to a furtherconfiguration of the aluminium alloy strip with an Mg content of 4.2 wt.% to 4.4 wt. %.

In order to provide the strength properties necessary for the areas ofapplication, the aluminium alloy strip according to a next embodimenthas a thickness of 0.5 mm to 4 mm. The thickness is preferably 1 mm to2.5 mm, since most of the areas of application of the aluminium alloystrip fall within this range.

Finally, in the automotive sector the aluminium alloy strip according tothe invention allows areas of application wherein the aluminium alloystrip in the soft state has a yield point R_(p0.2) of at least 110 MPaand a tensile strength R_(m) of at least 255 MPa. It has been found thataluminium alloy strips with such yield points and tensile strengthsespecially are particularly well-suited for use in the automotivesector.

According to a second teaching of the present invention the object shownabove is achieved by a method for producing an aluminium alloy stripaccording to the embodiments described above, wherein the methodcomprises the following process steps:

-   -   casting a rolling ingot preferably in the DC continuous casting        process;    -   homogenisation of the rolling ingot at 480° C. to 550° C. for at        least 0.5 hours;    -   hot rolling of the rolling ingot at a temperature of 280° C. to        500° C.;    -   cold rolling of the aluminium alloy strip to the final thickness        with a degree of rolling of 40% to 70% or 50% to 60%; and    -   soft annealing of the finished rolled aluminium alloy strip at        300° C. to 500° C. in a continuous furnace.

It has been found that with the indicated parameters in conjunction withthe stated aluminium alloying components an aluminium alloy strip withaverage grain sizes of 15 μm-30 μm can be produced, having sufficientresistance to intercrystalline corrosion, providing sufficient strengthproperties and also having very good forming properties, so thatlarge-area, deep-drawn sheet metal parts can be produced. Homogenisationof the rolling ingot ensures a homogenous structure and a homogenousdistribution of the alloying elements in the hot rolling ingots to berolled. The hot rolling at temperatures of 280° C.-500° C. allowsrecrystallization throughout during hot rolling, wherein the hot rollingtypically is performed up to a thickness of 2.8 mm-8 mm. The finalcold-rolling step is restricted to a degree of rolling of 40% to 70% or50% to 60%, in both cases in order to ensure recrystallizationthroughout the aluminium alloy strip during soft annealing. The higherthe degree of rolling of the aluminium alloy strip, the lower theaverage grain sizes become, wherein it has been found that above a 70%degree of rolling in the final soft annealing an average grain size canresult that is too low. At a degree of rolling below 40% during softannealing the average grain sizes are on the other hand too large, sothat despite the resistance to intercrystalline corrosion increasing,the formability is nevertheless reduced. Soft annealing of thefinish-rolled aluminium alloy strip takes place in a continuous furnace,which will normally have a heat-up rate of 1-10° C./second and so unlikea chamber furnace, in which an entire coil is heated, because of therapid heating will have a marked effect on the later properties of thestructure of the aluminium alloy strip. In particular, it has beenpossible to establish that during soft annealing in the continuousfurnace an improved formability of the strip compared to variantsannealed in the chamber furnace is achieved.

Alternatively, according to a further embodiment of the method, thealuminium alloy strip can also be produced with an intermediateannealing. According to this alternative variant after hot rollingalternatively the following process steps are performed:

-   -   cold rolling of the hot-rolled aluminium alloy strip to an        intermediate thickness which is determined in such a way that        the final degree of cold rolling to the final thickness is 40%        to 70% or 50% to 60%;    -   intermediate annealing of the aluminium alloy strip at 300° C.        to 500° C.;    -   cold rolling of the aluminium alloy strip to the final thickness        with a degree of rolling of 40% to 70% or 50% to 60%;    -   soft annealing of the finish-rolled aluminium alloy strip at        300° C. to 500° C. in a continuous furnace.

The intermediate annealing of the aluminium alloy strip can take placeboth in the chamber furnace and in the continuous furnace. An effect onformability could not be determined. The decisive factors here are thedegree of rolling achieved in cold rolling to the final thickness and ifthe soft annealing of the strip takes place in the continuous furnace.This determines the formability and corrosion resistance in conjunctionwith the alloying composition, irrespective of the type of intermediateannealing.

In order to prevent a further change in the microstructural state in thecoiled condition following soft annealing, the aluminium alloy stripaccording to a further configuration of the method is cooled after softannealing to a maximum temperature of 100° C., preferably a maximum of70° C. and then coiled.

As already stated above, the intermediate annealing can be carried outin a further configuration of the method in a batch furnace or in acontinuous furnace.

If the aluminium alloy strip is cold-rolled to a final thickness of 0.5mm-4 mm, preferably to a final thickness of 1 mm-2.5 mm, this providesthe typical areas of application, in particular automotive construction,with sheet metal with very good formability, and which can be deep-drawnwith large surface areas and at the same time provide high strengthproperties together with sufficient corrosion resistance tointercrystalline corrosion.

The soft annealing is preferably performed in the continuous furnace ata metal temperature of 350° C.-550° C., preferably at 400° C.-450° C.for 10 seconds to 5 minutes, preferably 20 seconds to 1 minute. Thisallows the cold rolled strip to recrystallize sufficiently thoroughlyand the corresponding properties with regard to the very goodformability and the average grain size to be achieved reliably andeconomically.

Finally, the object indicated above is achieved by a component for amotor vehicle, composed of the aluminium alloy strip according to theinvention. The components are characterised in that, as already stated,they can be deep-drawn with a large surface area and therefore forexample large-area components for automotive construction can beprovided. Furthermore, because of the strength properties provided thesealso have the necessary stiffness and the corrosion resistance requiredfor use in automotive construction.

It is conceivable, for example, for the component according to a furtherconfiguration to be a motor vehicle body part or body accessory, whichapart from being subject to high strength requirements is alsoheat-stressed. Preferably, the body-in-white parts such as an internaldoor part or an internal tailgate part, are made from the aluminiumalloy strip according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with the help of thedrawing. The drawing shows as follows:

FIG. 1 shows a schematic flow diagram of an embodiment of the productionmethod of the aluminium alloy strip.

FIG. 2 a shows a top view of the specimen geometry for the plane-straincupping test according to DIN EN ISO 12004.

FIG. 2 b shows a side-view of the schematic test set-up for theplane-strain cupping test according to DIN EN ISO 12004.

FIG. 3 shows a sectional view of the test setup for the SZ32 stretchdrawing measurements in the Erichsen cupping test according to DIN ENISO 20482.

FIG. 4 shows a typical embodiment of a large-area, deep-drawn sheetmetal part according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the sequence of embodiments for the production of aluminiumstrips.

The flow diagram of FIG. 1 is a schematic representation of the variousprocess steps of the production process of the aluminium alloy stripaccording to the invention.

In step 1, a rolling ingot of an AlMg aluminium alloy with the followingalloying elements is cast, for example in DC continuous casting:

-   -   Si≦0.2 wt. %.    -   Fe≦0.35 wt. %,    -   Cu≦0.15 wt. %,

0.2 wt. %≦Mn≦0.35 wt. %, 4.1 wt. %≦Mg≦4.5 wt. %,

-   -   Cr≦0.1 wt. %,    -   Zn≦0.25 wt. %,    -   Ti≦0.1 wt. %,        the remainder being Al and inevitable impurities, amounting to a        maximum of 0.05 wt. % individually and a maximum of 0.15 wt. %        in total.

Then the rolling ingot in process step 2 undergoes homogenisation, whichcan be performed in one or more stages. During homogenisation,temperatures of the rolling ingot of 480 to 550° C. are reached for atleast 0.5 hours. In process step 3 the rolling ingot is then hot rolled,wherein typically temperatures of 280° C. to 500° C. are reached. Thefinal thicknesses of the hot-rolled strip are for example 2.8 to 8 mm.The hot-rolled strip thickness can be selected such that after hotrolling only a single cold rolling step 4 takes place, in which thehot-rolled strip, with a degree of rolling of 40% to 70%, preferably 50%to 60%, has its thickness reduced to the final thickness.

Then the aluminium alloy strip that has been cold-rolled to its finalthickness undergoes soft annealing. According to the invention the softannealing is performed in a continuous furnace. In the embodiments shownin Table 1, the second route was applied with an intermediate annealing.For this, the hot-rolled strip after hot rolling according to processstep 3 is passed for cold rolling 4 a, in which the aluminium alloystrip is cold rolled to an intermediate thickness, which is determinedin such a way that the final degree of cold rolling to the finalthickness is 40% to 70% or 50% to 60%. In a subsequent intermediateannealing the aluminium alloy strip preferably recrystallizesthroughout. The intermediate annealing was carried out in theembodiments either in the continuous furnace at 400° C. to 450° C. or inthe chamber furnace at 330° C. to 380° C.

The intermediate annealing is shown in FIG. 1 by process step 4 b. Inprocess step 4 c according to FIG. 1 the intermediately-annealedaluminium alloy strip is finally passed for cold rolling to the finalthickness, wherein the degree of rolling in process step 4 c is between40% and 70%, preferably between 50% and 60%. Then the aluminium alloystrip is again converted to the soft state by soft annealing, whereinaccording to the invention the soft annealing is carried out in thecontinuous furnace at 400° C. to 450° C. The annealings of thecomparative examples in table 4 were carried out in the chamber furnace(KO) at 330° C. to 380° C. During the various trials, apart from thedifferent aluminium alloys various degrees of rolling after theintermediate annealing were set. The values for the degree of rollingafter the intermediate annealing are likewise shown in Tables 1 and 4.The average grain size of the soft-annealed aluminium alloy strip wasalso measured. To this end, longitudinal sections were anodisedaccording to the Barker method and then measured under the microscopeaccording to ASTM E1382 and the average grain size determined from theaverage grain diameter.

The aluminium alloy strips manufactured in this way had their mechanicalcharacteristics determined, in particular the yield point R_(p0.2), thetensile strength R_(m), the uniform elongation Ag and the elongation atrupture A_(80mm), Tables 2, 5. Apart from the mechanical characteristicsof the aluminium alloy strips measured according to EN 10002-1 or ISO6892 in addition the average grain sizes according to ASTM E1382 in μmare given. Furthermore, the corrosion resistance to intercrystallinecorrosion in accordance with ASTM G67 was measured, and in fact withoutadditional heat treatment in the initial state (at 0 h). In order tosimulate use in a motor vehicle, the aluminium alloy strips, prior tothe corrosion test, furthermore underwent various heat treatments. Afirst heat treatment consisted of storage of the aluminium strips for 20minutes at 185° C., in order to model the CDP cycle.

In a further series of measurements the aluminium alloy strips were alsostored for 200 hours or 500 hours at 80° C. and then underwent thecorrosion test. Since the forming of aluminium alloy strips or sheetscan also affect the corrosion resistance, the aluminium alloy stripswere stretched in a further trial by approximately 15%, and underwentheat treatment or storage at raised temperature and then a test forintercrystalline corrosion according to ASTM G67, during which the massloss was measured.

Table 1 gives the alloying contents of a total of four differentaluminium alloys, which fall within the specification of the AA5182-typealuminium alloy. The reference alloy is constituted by the material usedto date and is shown in comparison to variants 1, 2 and 3. Table 1 alsocontains details of the type of final annealing, the final degree ofrolling and the measured average grain size (grain size diameter) in μm.Variants 1 and 2 differ here merely in terms of final degree of rolling,which leads to the formation of a different grain size. Thus variant 2differs from variant 1 irrespective of the almost identical alloyingelements essentially in terms of the final degree of rolling of 57% atidentical continuous furnace conditions. The result was that variant 2had an average grain size of 18 μm compared to 33 μm for variant 1. Thestrips in Table 1 were heated in the continuous furnace for 20 secondsto 1 minute to a temperature of 400° C. to 450° C., then cooled andcoiled at less than 100° C. The specimens taken were then, as indicatedin Table 2, measured according to the corresponding DIN EN ISOstandards.

It is clear from Table 2 that variant 1 in terms of the yield point doesnot reliably reach the value of 110 MPa and in the diagonal measurement,identified by the D symbol, has a value of less than 110 MPa. Themeasurement in the direction of rolling L and transversally to thedirection of rolling Q showed, however, that variant 1 actually reacheda yield point R_(p0.2) of 110 MPa. The reference and variants 2 and 3were significantly above this lower limit for the yield point. Theembodiment according to the invention in variant 2 reliably achieved theyield point value of 110 M Pa in all tensile directions. It is clear tosee that variant 3 with the highest Mg content of 4.95 wt. % achievesthe highest yield point and tensile strength figures. It can also beseen that the different degree of rolling between variants 1 and 2 notonly markedly influences the grain size, but in particular raises theyield point to a value of significantly higher than 110 MPa.

In particular the alloy according to the invention in variant 2 has alower anisotropy compared to the reference, reflected in lower values ofthe planar anisotropy Ar. Here, the planar anisotropy Δr is defined as½*(r_(L)+r_(Q)−2 r_(D)), wherein r_(L), r_(Q) and r_(D) correspond tothe r-values in the longitudinal, traversal and/or diagonal direction.Here, the average r-value F, calculated from ¼*(r_(L)+r_(Q)+2r_(D)),does not differ significantly from that of the reference material.

Table 3 gives the measured values recorded in relation to the resistanceto intercrystalline corrosion. It can be seen that variant 2 accordingto the invention in terms of the measured values of the reference, inparticular in respect of the long-time stressing, has comparable valuesboth in the stretched state and in the unstretched state. Here variant 2and the reference are almost identical. Variant 3, which despite thehaving the highest yield point values and tensile strength values,nevertheless in the corrosion test demonstrated that an excessive Mgcontent results in an excessive mass loss, in particular in thelong-time tests, which apart from a short temperature cycle of 20minutes at 185° C. also include long-time stressing of 200 hours at 80°C.

With regard to the measured values in Table 3 regarding the formabilityit can be seen that in particular variant 2 was superior in terms of thestretch forming properties in the SZ32 cupping test and in theplane-strain cupping test to the reference alloy. The clear improvementin forming behaviour of the aluminium alloy strip according to variant 2compared to the reference aluminium alloy strip shows that even with areduced Mg content comparable yield point values and tensile strengthvales could be achieved with the reference alloy, without major lossesin resistance to intercrystalline corrosion. This was demonstrated inparticular by the mass loss measurement performed according to ASTM G67in the NAML test. Significantly, with variant 2 an improvement in thedeep drawing behaviour in the Erichsen cupping test by 7% and in theplane-strain cupping tests by approximately 10% was found, demonstratingthe additional forming potential of the aluminium alloy strip accordingto the invention. This additional forming potential can be used toproduce deep-drawn, large-area sheet metal parts, for example internaldoor parts of a motor car.

A brief explanation of the test setup for the “SZ32 cupping” testaccording to DIN EN ISO 20482 and the plane-strain cupping test withNakajima geometry according to DIN EN ISO 12004 is provided below.

FIG. 2 a shows the geometry of test piece 1. From a circular sheet metalcut-out the tapered test piece 1 is cut such that the web 4 has a widthof 100 mm and the radii 2 at the waisted parts are 20 mm. Dimension 3,which is 100 mm, represents the diameter of the punch. FIG. 2 b showsthe test piece 1 clamped between two holders 5, 6. The test piece 1,which was placed on a mount 8 and via the holders 5, 6 pushed againstthe support, is pulled with a punch 7, having a semi-circular tip with aradius of 100 mm, in the direction of the arrow. The holders also haveentry radii of 5 or 10 mm on their side facing the mount 8. The forcewith which the cupping test is performed is measured during the formingand a sudden drop in load, signalling the formation of a crack, leads tothe measurement of the corresponding punching depth.

The “SZ32 cupping” test according to Erichsen has a similar setup, butno wasted test pieces are used, however. Here, a test piece 9 is simplyheld between a holder 10 and a support 11 and drawn with a punch 12until likewise a drop is measured in the load of the drawing force.Then, again, the corresponding position of the punch is measured. Theopening of the dies in FIG. 3 was 35.4 mm and the punch diameter 32 mm,meaning that the punch radius was 16 mm. A Teflon deep-drawing film wasalso used to reduce friction in the SZ32 deep-drawing test.

In Tables 4 and 5, further embodiments and comparative examples werecreated and measured according to their mechanical characteristics andtheir resistance to intercrystalline corrosion. It can be seen that thecombination of using the continuous furnace and a specifically selectedgrain size of 15 μm-30 μm, preferably of 15 μm-25 μm results in a goodcompromise between corrosion resistance and mechanical measured values.Thus, for example, the embodiments according to the invention Nos. 3, 4,7 and 11 have a satisfactory resistance to intercrystalline corrosionand also exhibit the mechanical measured values R_(p0.2) and R_(m)necessary for use in the automotive sector, so that these are ideal forthe provision of large-area, deep-drawn components.

FIG. 4 shows as an example a corresponding body-in-white part in theform of an interior part of a door, which by using the aluminium alloystrip of the present invention can be produced from a single deep-drawnsheet. Here, the sheet thickness is preferably 1.0-2.5 mm. Furthermore,other parts of a motor vehicle are conceivable in sheet metal shellconstruction, such as the interior parts of tailgates, bonnets, andcomponents in the vehicle structure, which are subject to stringentrequirements in terms of formability and intercrystalline corrosion.

TABLE 1 Final degree Material [wt. %] Final of rolling (cold Grain Si FeCu Mn Mg Cr Zn Ti Impurities annealing rolling) size [μm] min. 0.20 4.0Individually max. AA 5182 0.20 0.35 0.15 0.50 5.0 0.10 0.25 0.10 0.05 intotal max. max. 0.15 Reference 0.07 0.24 0.036 0.3 4.57 0.005 0.0070.016 0.05 BDLO 46 15 0.15 Var. 1 0.06 0.16 0.004 0.27 4.37 0.008 0.0020.013 0.05 BDLO 21 33 0.15 Var. 2 0.06 0.16 0.004 0.27 4.38 0.008 0.0030.013 0.05 BDLO 57 18 0.15 Var. 3 0.05 0.17 0.023 0.26 4.95 0.008 0.0030.026 0.05 BDLO 57 17 0.15

TABLE 2 Test R_(p0.2) Rm Ag Ag (elong) A_(80 mm) A_(80 mm) (Hand)Z-value piece Pos. N/mm² N/mm² % % % % % n-value r-value Δr r Ref. L 137284 21.3 20.7 24.5 25.2 69 0.316 0.827 0.197 0.754 T 133 276 22.2 21.425.2 25.8 72 0.306 0.704 D 133 277 21.9 21.6 25.5 26.3 71 0.305 0.779Var. 1 L 110 262 21.2 21.9 25.9 26.4 71 0.335 0.668 −0.363 0.779 T 107256 24.7 23.0 27.7 28.7 72 0.338 0.870 D 111 259 22.0 21.2 24.6 25.7 650.332 0.708 Var. 2 L 128 266 23.2 22.7 26.8 27.7 67 0.332 0.724 0.0350.693 T 127 261 23.1 22.2 26.2 27.0 67 0.332 0.685 D 128 262 23.9 22.526.5 27.6 66 0.333 0.681 Var. 3 L 141 290 24.1 23.5 28.4 29.1 70 0.3350.697 −0.12 0.710 T 140 286 22.6 23.4 27.0 27.8 68 0.336 0.740 D 141 28622.6 23.3 27.1 27.7 65 0.335 0.663 DIN EN ISO 6892-1:2009 DIN EN ISO DINEN ISO 10113:2009 10275:2009

TABLE 3 IK-mass losses Formability Not 20 min 185° C. 15% stretched 15%stretched SZ32 Plane-strain thermally 20 min. plus 200 h 17 h 20 min. 20min. 185° C. plus cupping cupping Variant treated 185° C. 80° C. 130° C.185° C. 200 h 80° C. [mm] [mm] Limit 2.0 4.0 35.0 50.0 15.0 45.0Reference 1.2 2.1 29.8 48.8 10.4 42.1 14.2 27.9 Var. 1 (comp.) 1.2 1.710.4 21.3 4.4 12.9 14.5 30.3 Var. 2 (inv.) 1.2 2.4 33.7 42.2 13.5 40.114.6 30.7 Var. 3 (comp.) 1.3 5.3 41.7 55.0 30.4 53.5 14.6 31.6

TABLE 4 Grain Degree of Final size No Alloy rolling [%] annealing [μm]Si Fe Cu Mn Mg Cr Zn Ti 1 III 46 KO 16 0.07 0.24 0.040 0.30 4.50 0.0050.007 0.016 3 II 57 BOLO 18 0.06 0.16 0.004 0.27 4.35 0.008 0.002 0.0134 I 45 BOLO 18 0.03 0.13 0.002 0.25 4.15 0.001 0.004 0.021 6 I 45 KO 210.03 0.13 0.002 0.25 4.15 0.001 0.004 0.021 7 III 30 BOLO 22 0.07 0.240.040 0.30 4.50 0.005 0.007 0.016 11 III 25 BOLO 27 0.07 0.24 0.040 0.304.50 0.005 0.007 0.016 13 I 32 BOLO 29 0.03 0.13 0.002 0.25 4.15 0.0010.004 0.021 15 III 30 KO 30 0.07 0.24 0.040 0.30 4.50 0.005 0.007 0.01616 I 25 BOLO 31 0.03 0.13 0.002 0.25 4.15 0.001 0.004 0.021 18 II 21BOLO 33 0.06 0.16 0.004 0.27 4.35 0.008 0.002 0.013 20 I 20 BOLO 34 0.030.13 0.002 0.25 4.15 0.001 0.004 0.021

TABLE 5 IK-mass loss, Mechanical IK-mass loss, unstretched** 15%stretched** characteristics, 20 min. 20 Min. 185° C. + 20 Min. 185° C. +20 Min. 20 Min. 185° C. + soft state No Start (O h) 185° C. 200 h 80° C.500 h/80° C. 185° C. 200 h 80° C. R_(p0.2) Rm Ag A_(80 mm) Result 1 III15.4 16.6 25.7 26.9 18.8 33.6 135 279 20.7 25.2 Comparison 3 II 1.2 2.433.7 36.7 13.5 40.1 128 262 23.9 26.5 Invention 4 I 1.3 1.9 17.8 22.21.6 20.1 117 258 22.8 25.3 Invention 6 I 8.2 10.8 18.6 22.1 9.6 20.7 106250 23.8 26.7 Comparison 7 III 1.1 1.7 18.0 24.5 3.3 25.1 119 276 20.324.9 Invention 11 III 1.1 1.6 14.3 17.7 2.8 19.8 116 275 20.2 24.4Invention 13 I 1.1 1.2 13.3 16.7 2.1 17.4 104 251 22.2 24.8 Comparison15 III 2.8 3.0 7.9 10.9 6.4 18.0 125 281 19.5 23.6 Comparison 16 I 1.11.3 10.8 13.1 1.9 14.2 103 252 21.6 26.1 Comparison 18 II 1.2 1.7 10.412.5 4.4 12.9 109 259 22.0 24.6 Comparison 20 I 1.1 1.2 8.3 11.1 1.712.4 101 251 20.8 25.1 Comparison

1. Cold-rolled aluminium alloy strip composed of an AlMg aluminiumalloy, wherein the aluminium alloy comprises the following alloyingelements: Si≦0.2 wt. %, Fe≦0.35 wt. %, Cu≦0.15 wt. %, 0.2 wt. %≦Mn≦0.35wt. %, 4.1 wt. %≦Mg≦4.5 wt. %, Cr≦0.1 wt. %, Zn≦0.25 wt. %, Ti≦0.1 wt.%, the remainder being Al and inevitable impurities, amounting to amaximum of 0.05 wt. % individually and to a maximum of 0.15 wt. % intotal, wherein the aluminium alloy strip has a recrystallizedmicrostructure, the grain size of the microstructure ranges from 15 μmto 25 μm and the final soft annealing of the aluminium alloy strip isperformed in a continuous furnace.
 2. The Aluminium alloy stripaccording to claim 1, wherein the aluminium alloy also has one or moreof the following restrictions to the contents of alloying elements: 0.03wt. % Si≦0.10 wt. %, Cu≦0.1, Cr≦0.05 wt. %, Zn≦0.05 wt. %, 0.01 wt.%≦Ti≦0.05 wt. %.
 3. The Aluminium alloy strip according to claim 1,wherein the aluminium alloy also has one or more of the followingrestrictions to the contents of alloying elements: Cr≦0.02 wt. %,Zn≦0.02 wt. %.
 4. The Aluminium alloy strip according to claim 1,wherein the Fe content is 0.10 wt. % to 0.25 wt. % or 0.10 wt. % to 0.2wt. %.
 5. The Aluminium alloy strip according to claim 1, wherein the Mncontent is 0.20 wt. % to 0.30 wt. %.
 6. The Aluminium alloy stripaccording to claim 1, wherein the Mg content is 4.2 wt. % to 4.4 wt. %.7. The Aluminium alloy strip according to claim 1, wherein the aluminiumalloy strip has a thickness of 0.5 mm to 4 mm.
 8. The Aluminium alloystrip according to claim 1, wherein the aluminium alloy strip in thesoft state has a yield point R_(p0.2) of at least 110 MPa and a tensilestrength R_(m) of at least 255 MPa.
 9. A Method for producing analuminium alloy strip according to claim 1 comprising the followingprocess steps: casting a rolling ingot; homogenisation of the rollingingot at 480° C. to 550° C. for at least 0.5 hours; hot rolling of therolling ingot at a temperature of 280° C. to 500° C.; cold rolling ofthe aluminium alloy strip to the final thickness with a degree ofrolling of 40% to 70% or 50% to 60%; and soft annealing of thefinished-rolled aluminium alloy strip at 300° C. to 500° C. in acontinuous furnace.
 10. The Method according to claim 9, wherein afterhot rolling alternatively the following process steps are performed:cold rolling of the hot-rolled aluminium alloy strip to an intermediatethickness which is determined in such a way that the final degree ofcold rolling to the final thickness is 40% to 70% or 50% to 60%;intermediate annealing of the aluminium alloy strip at 300° C. to 500°C.; cold rolling of the aluminium alloy strip to the final thicknesswith a degree of rolling of 40% to 70% or 50% to 60%; soft annealing ofthe finish-rolled aluminium alloy strip at 300° C.-500° C. in acontinuous furnace.
 11. The Method according to claim 9, whereinaluminium alloy strip after soft annealing is cooled to a maximumtemperature of 100° C. and then coiled.
 12. The Method according toclaim 10, wherein the intermediate annealing is performed in a batchfurnace or in a continuous furnace.
 13. The Method according to claim 9,wherein the aluminium alloy strip is cold rolled to a final thickness of0.5 mm to 4 mm.
 14. Method according to claim 9, wherein the softannealing is performed in the continuous furnace at a metal temperatureof 350° C. to 550° C. for 10 seconds to 5 minutes.
 15. A Component for amotor vehicle, composed of an aluminium alloy strip according toclaim
 1. 16. The Component according to claim 15, wherein the componentis a body part or a body accessory of a motor vehicle.